1. Field of the Invention
This invention relates to a camera and more particularly to an improvement in the method of supporting a motor incorporated in a structural body of the camera.
2. Description of the Related Art
The cameras of the kind performing film feeding, shutter charging, and mirror driving actions by means of motors have been proposed. FIG. 2 shows by way of example the arrangement of the conventional single-lens reflex camera for performing shutter charging and mirror driving actions with a motor.
The motor 2 is fixed by screws 3 to a structural member 1 of the camera body. The power (or driving force) of the motor 2 is transmitted to a gear 5 by a pinion gear 4, which is attached to the output shaft 2a of the motor 2. The motor power is moderated through gears 6, 7 and 8, a power transmission shaft 9 and a worm gear 10 before the motor power reaches cam gears 11 and 12.
The cam gear 11 is provided for driving the mirror of the single-lens reflex camera. When the cam gear 11 rotates counterclockwise, the fore end 13a of a lever 13 comes off the cam top of the cam gear 11. Then, the lever 13 is turned counterclockwise to move upward a mirror member (not shown) to a photographing-standby position. At this moment, the cam gear 12, which is provided for charging the shutter of the camera, rotates clockwise. A roller 17b mounted on a lever 17, which is arranged to charge the shutter, then moves from the cam top of the cam gear 12 to the bottom part thereof. Another roller 17a of the lever 17 moves downward from a shutter-charging-completed position to a photographing-standby position. A photograph can be taken by stopping the motor 2 under this condition. After that, the mirror is caused to move downward by restarting the motor 2 to rotate the cam gear 11 counterclockwise and causing the lever 13 to turn clockwise. At the same time, the shutter charged with the lever 17 is caused to turn counterclockwise to move the roller 17a upward by rotating the cam gear 12 clockwise.
The power transmission mechanism of the camera, which is arranged in this manner, however, has presented a problem in that the vibrations of the motor are transmitted to structural members and thus cause vibrations and noises of the camera, because the motor 2 is fixed directly to the structural member 1 in the camera body.
It has been known that many cameras are provided with a built-in electric motor for film feeding with the driving force of the motor. In these cameras, the parts included in such a driving system are all attached directly to a structural body with screws or the like as discrete parts or units.
FIG. 16 is an oblique view showing by way of example a camera having a film feeding mechanism arranged to be driven by a motor. FIG. 17 is a sectional view showing how essential parts are arranged in the mechanism. A driving unit 1201 consists of a small motor, which is a drive source, and all the speed-reduction and power-transmission mechanisms. The driving unit 1201 is secured by several screws 1202 to a camera body 1200, which is the structural body of the camera. An upper base plate 1106 is secured by screws to the upper part of a spool chamber 1200a a which is formed in the body 1200. A spool 1204 is disposed within the spool chamber 1200a and is arranged to be rotatable on the same axis as a gear 1214 of the driving unit 1201 with the spool 1204 fittingly engaged with a boss 1106a of the upper base plate 1106 and a claw 1214a formed on the gear 1214. The movement of the spool 1204 in the direction of thrust is restricted by the upper base plate 1106 and the gear 1214.
Many camera parts in recent years are made of plastics for reduction in weight and cost. The structural body such as the above-stated camera body 1200 is mostly made of a plastic material instead of zinc or aluminum.
With the driving unit 1201 attached directly to the body 1200 as in the case of FIG. 16, vibrations generated by the motor 1003 and the speed-reduction mechanism are transferred directly to the body 1200 when the driving unit 1201 is in action. In a case where the body 1200 is made of a plastic material in a complex shape, in particular, the vibrations tend to bring forth unpleasant noises.
Therefore, it has been contrived, as one of means for reducing such noises of the camera, to insert a vibration absorber having a low Young's modulus such as butyl rubber between the body 1200 and the driving unit 1201. However, the use of the vibration absorber makes it difficult to reliably keep the driving unit 1201 in position. Under a film feeding load, the driving unit 1201 tends to vibrate by deforming the vibration absorber. If a harder vibration absorber is used to prevent the deformation, the effect of preventing the transfer of vibration would be lowered.
With the spool 1204 arranged to be set in place simply by the gear 1214 of the driving unit 1201 and the upper base plate 1106, therefore, the axis of rotation of the spool 1204 becomes unstable due to the load and driving force applied to the spool 1204 at the time of film feeding, and a film winding action might not be adequately accomplished.
FIG. 25 shows by way of example another camera having a driving unit provided with a timing belt. In FIG. 25, a reference numeral 2101' denotes the driving unit. The driving unit 2101' includes a small motor which serves as a drive source and has all the speed-reduction and transmission functions for the power of the motor. The driving unit 2101 is mounted on the body 2100 of the camera in one unified body. The gear 2014 of the driving unit 2101' is arranged to be fitted on a spool 2104 and to transmit a film winding driving force to the spool 2104. A film rewinding fork 2019 protrudes into a film cartridge chamber 2100b and is arranged to be constantly engaging a projection provided within a cartridge shaft 2113 with the cartridge 2114 in a loaded state.
When the driving unit 2101' is winding the film 2112, the driving force of the motor 2003 is moderated by a gear train (not shown) mounted on a gear base plate 2002. The driving force is transmitted to the gear 2014 after the output direction of the driving force is switched by a planetary gear mechanism (not shown).
Therefore, the spool 2104 is rotated in the direction of arrow Wd. The film 2112 is gradually taken up onto the periphery of the spool 2104 with its perforation hole 2112a hooked by the claws 2104a of the spool 2104.
When the driving unit 2101' is in a rewinding condition, the planetary gear mechanism transmits the driving force of a motor 2003 to a gear 2016a. A pulley 2016b is formed in one unified body with the gear 2016a. The driving force is transmitted to a pulley 2018 through a timing belt 2017, which is put on the pulley 2016b. The above-stated fork 2019 engages the pulley 2018 and is arranged to rotate together with the pulley 2018. The film 2112 can be stowed inside the cartridge 2114 by rotating the cartridge shaft 2113 in the direction of arrow Wf.
In the case of the arrangement shown in FIG. 25, the cartridge shaft 2113 is caused by the tensile force of the film 2112 to rotate in the direction of arrow We when winding the film. However, a series of gear train from the pulley 2018 to a part at which disengagement is caused by the planetary gear mechanism including the timing belt 2017 acts as a load on the cartridge shaft 2113 which engages the fork 2019.
Without keeping the blank (unloaded) rotation torque of the above-stated part low, therefore, the arrangement would bring forth a large consumption current at the time of film winding. Film feeding might become impossible in the worst case. In a case where a timing belt is used, in particular, it must be taken into consideration that the load on the rotating force is greatly influenced by a belt stretching force called an initial tension. FIG. 26 shows in a plan view the layout of the pulleys 2016b and 2018 and the timing belt 2017. The initial tension can be lowered by setting a distance L between axes at a shorter distance than a theoretical distance computed from the layout of the pulleys and the peripheral length of the belt 2017. However, if the timing belt 2017 is used in a very slack state, the actual application of a driving force to the belt tends to bring about the following problem:
Referring to FIG. 26, when a driving force is applied to the pulley 2016b in the direction of arrow Wf in rewinding the film, a tension T is generated on one side of the belt 2017 on which an idler 2023 is disposed, i.e., on the so-called driving side of the timing belt 2017. However, since no driving force is exerted on the other side of the timing belt 2017, no tension arises there. As a result, slackness arises at a belt part where the timing belt 2017 engages the pulley 2018 as indicated with an arrow Y. This phenomenon more saliently arises accordingly as the tension T is increased by a load on the pulley 2018 and is, of course, more apt to arise accordingly as the initial tension of the timing belt 2017 is weaker.
When the slack at the part engaging the pulley 2018 becomes excessive, the number of engaging teeth of the pulleys 2016b and 2018 with the timing belt 2017 decreases, so that the engaging parts of them come to disengage becoming no longer capable of bearing the driving force, and there takes place the so-called tooth slippage.
FIG. 27 shows one example of the arrangement of preventing the tooth slippage, which is generally employed. In this case, a tension is given also on the slackening side of the timing belt 2017 by applying the urging force of a spring 2203 to a roller 2202 in the direction of arrow so that the tooth slippage can be prevented. This arrangement is, however, not adoptable because it is against the theme of lowering the initial tension mentioned in the foregoing.
FIG. 28 shows another example of the arrangement of preventing the tooth slippage, which is generally employed. In that case, a fixed roller 2204 is disposed on the inner side of a tangential line S, which connects the outer peripheral parts of both ends of the timing belt 2017. The provision of the roller 2204 effectively prevents the timing belt 2017 from slackening in the direction of arrow F, so that the amount of slackening at the part indicated by the arrow Y can be lessened more effectively than the example shown in FIG. 26.
However, the total length of the timing belt 2017 varies due to unevenness of manufacture and changes of temperature. It is extremely difficult to find such a layout that is apposite to the above-stated roller 2204 and yet allows to have a low initial tension. Besides, it is possible in some cases that the initial tension might be increased by the roller 2204. Therefore, that arrangement is also hardly adoptable.
FIG. 29 shows a further example of the art for preventing the tooth slippage in a manner different from the arrangement shown in FIGS. 27 and 28. Referring to FIG. 29, rollers 2205 and 2208 are arranged to push the timing belt 2017 from outside in the direction of normal lines at parts where the timing belt 2017 engages the pulleys 2016b and 2018 and where a slack takes place at the time of driving, so that the timing belt 2017 can be prevented from disengaging at the time of driving. The rollers 2205 and 2208 are urged to push the timing belt 2017 by a torsion spring 2207 and a leaf spring 2209 or the like.
In accordance with this arrangement, the layout of the rollers can be made with the initial tension of the timing belt 2017 set at a fairly low value, because the initial tension is not affected by the arrangement at all.
However, since the timing belt 2017 is pushed by the rollers 2205 and 2208, some load is imposed on the force of rotation. In addition to that, the arrangement causes an increase in the number of component parts, which is undesirable in terms of a reduction in cost.